batman-adv: Distributed ARP Table - implement local storage

Since batman-adv cannot inter-operate with the host ARP table, this patch
introduces a batman-adv private storage for ARP entries exchanged within DAT.
This storage will represent the node local cache in the DAT protocol.

Signed-off-by: Antonio Quartulli <ordex@autistici.org>
diff --git a/net/batman-adv/main.h b/net/batman-adv/main.h
index 5699f2b..25adfd2 100644
--- a/net/batman-adv/main.h
+++ b/net/batman-adv/main.h
@@ -44,6 +44,7 @@
 #define BATADV_TT_LOCAL_TIMEOUT 3600000 /* in milliseconds */
 #define BATADV_TT_CLIENT_ROAM_TIMEOUT 600000 /* in milliseconds */
 #define BATADV_TT_CLIENT_TEMP_TIMEOUT 600000 /* in milliseconds */
+#define BATADV_DAT_ENTRY_TIMEOUT (5*60000) /* 5 mins in milliseconds */
 /* sliding packet range of received originator messages in sequence numbers
  * (should be a multiple of our word size)
  */